Cooled vane

ABSTRACT

An air cooled stator vane or the like for a gas turbine engine is constructed to include a plurality of axially and radially spaced pockets formed on the outer surfaces of the airfoil sections. Air is directed into the pocket on one end of a passage defined by the pocket to impinge on the back wall of the pocket, change directions and flow through the passage and discharge into the gas path as a film of cooling air coalesced by slots formed at the end of the pocket. The outer wall can be cast in its entirety or fabricated from sheet metal sheaths supported to a cast inner shell. The pockets are fed cooling air through a central passage in the stator vane or through impingement inserts disposed in the central passage.

The invention was made under a U.S. Government contract and theGovernment has rights herein.

CROSS REFERENCE

The subject matter of this application is related to the subject matterof commonly assigned U.S. patent application Ser. No. 07/550,003 filedon even date herewith and entitled "Cooled Vane".

TECHNICAL FIELD

This invention relates to gas turbine engines and more particularly tothe cooling aspects of the vane and other stator components.

BACKGROUND ART

The technical community working in gas turbine engine technology haveand are continually expending considerable effort to improve the coolingaspects of the engine's component parts, particularly in the turbinearea. Obviously, improving the effectiveness of the cooling air resultsin either utilizing less air for cooling or operating the engine athigher temperature. Either situation attributes to an improvement in theperformance of the engine.

It is axiomatic that notwithstanding the enormous results anddevelopment that has occurred over the years the state-of-the-art filmcooling and convection techniques are not optimum.

Some of the problems that adversely affect the cooling aspectsparticularly in vanes are (1) the pressure ratio across all of the filmholes cannot be optimized and (2) in vanes that incorporate conventionalinserts, the static pressure downstream of the insert is substantiallyconstant. Essentially in item (1) above the holes that operate with lessthan optimum pressure drop fail to produce optimum film cooling and initem (2) above a constant stator pressure adversely affects internalconvection.

One of the techniques that has been used with some degree of success iscoating of the airfoil sections of the vanes with a well known thermalbarrier coating. However, a coated vane conventionally requires drillingthe film cooling hole after the coating process by a laser whichtypically results in a cylindrical hole compromising the film coolingeffectiveness. Moreover, flow control through the laser hole is moredifficult, presenting additional problems to the engine designer.

We have found that we can obviate the problems noted above and improvethe cooling effectiveness by providing in the vane a plurality ofpockets that form metering slots on the airfoil surface together withjudiciously located holes associated with each pocket for feedingcooling air to the metering slots which in turn effectively coalesce theair into a film of cooling air that flows across the external surface ofthe vane. The passageway from these located holes to the inclined slotsplaces the cooling air in indirect parallel flow heat exchange relationwith the gas path.

It is contemplated within the scope of this invention that the vane befabricated from either a total casting process or a partial castingprocess where a structural inner shell is cast and a sheath formed fromsheet metal encapsulates the shell.

A vane constructed in accordance with this invention affords amongstother advantages the following:

1) Film cooling effectiveness is optimized.

2) The film cooling system can adapt to thermal barrier coatings and thelike without film cooling compromise.

3) Convection is optimized since flow can be metered locally toheat-transfer requirements and overall pressure ratio.

4) In the sheet metal design a repair procedure can be accommodatedwhere distressed panels can be replaced without scrapping the totalpart.

5) A pressure side or suction side panel of the sheet metal designedvane may be optimized for flow and film coverage.

6) Improved cooling is achieved with hole and slot sizes that are largeenough to minimize internal plugging.

7) In the sheet metal configuration flexibility of material choices forthe external shell is significantly increased.

8) In the fully cast configuration the vane can be cast in halves whichoffer the most versatility in terms of achieving desired cooling flowsand film blowing parameters.

SUMMARY OF THE INVENTION

An object of this invention is to provide for a gas turbine engineimproved cooling effectiveness for the engine's vanes and/or statorcomponents.

A feature of this invention is to provide side walls that define theairfoil section of a vane having a plurality of pockets each having ametered slot for flowing film cooling air on the outer surface of theside wall and having judiciously located holes discreetly feedingcooling air into said pockets from a central passageway in the vanecommunicating with a source of cooling air. The airfoil surface in oneembodiment is formed from sheet metal supported from an inner cast shelland in another embodiment the vane including the airfoil section isfully cast. Still another embodiment employs a double layer of stampedsheet metal forming a 2-layer inner configuration. And still anotherembodiment includes a fully cast vane including pockets with judiciouslylocated holes as previously described, but also including inserts havinga plurality of apertures for feeding cooling air from the centralpassageway to the judiciously located holes.

The foregoing and other features and advantages of the present inventionwill become more apparent from the following description andaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial view in schematic of the combustor, 1st turbine andvane of a gas turbine engine exemplary of the prior art.

FIG. 2 is a sectional view taken along lines 2--2 of FIG. 1 of a priorart vane.

FIG. 3 is a sectional view of a vane made in accordance with thisinvention showing the details thereof.

FIG. 4 is a sectional view of the inventive vane disclosing one of thesteps in manufacturing.

FIG. 5 is an enlarged view showing a portion of the pressure surface ofthe airfoil section of the vane in FIG. 3.

FIG. 6 is a partial view of an enlarged section of one of the pockets inFIG. 5.

FIG. 7 is a sectional view of the airfoil section depicting anotherembodiment of a vane incorporating this invention.

FIG. 8 is a partial view of an enlarged section of the stamped sheetmetal including the pocket in FIG. 7.

FIG. 9 is a sectional view of another embodiment of a vane employingthis invention.

FIG. 10 is a partial view of an enlarged section of the stamped sheetmetal sheath including the pocket in FIG. 9.

FIG. 11 is an exploded view in perspective of the embodiment depicted inFIG. 7.

FIG. 12 is an exploded view identical to FIG. 11 but including theplatform.

BEST MODE FOR CARRYING OUT THE INVENTION

While in its preferred embodiment this invention is being utilized inthe first stage turbine stator vane of a gas turbine engine, it will beunderstood by those skilled in this technology that the invention can beemployed in other vanes and other static components without departingfrom the scope of this invention. Notwithstanding the fact that thepreferred embodiment is a fully cast vane utilizing inserts thepartially cast embodiment or fully cast embodiment without inserts areall deemed to be within the scope of this invention.

The invention can perhaps be best understood by first having anunderstanding of the state-of-the-art vane exemplified by the prior artdisclosed in FIGS. 1 and 2. As shown the vane generally indicated byreference numeral 10 is disposed between the turbine 12 and burner 14.The vane 10 is cooled by routing cool air obtained from the engine'scompressor section (not shown) via the passageways 16 and 18 which isdefined by the outer annular case 20 and outer liner 22 and innerannular case 24 and inner annular burner liner 26. Inserts 28 and 30opened at its base distribute the cool air from passageways 16 and 18through a plurality of holes formed in the walls thereof to a pluralityof holes formed in the pressure surface, suction surface, trailing andleading edges. Typically, flow entering the insert or impingement tubecircuit 28 from passageway 18 exits the vane as film air through filmholes in the leading edge 32, the pressure surface 34 and the suctionsurface 36. Flow entering the insert or impingement tube circuit 30 frompassageway 16 exits the vane as film air through film holes in thepressure surface 34 and suction surface 36 and as dump flow throughholes in the trailing edge 38. Platforms 35 and 37 on the inner andoutside diameter serve to attach the vane to the engine's turbine andcombustor cases and are opened to the compressor air flow.

What has been described is conventional in available gas turbine enginessuch as the 9D, PW2037, PW4000 and F100 family of engines manufacturedby Pratt and Whitney division of United Technologies Corporation, theassignee common with this patent application. For the sake ofconvenience and simplicity only that portion germane to the invention isdescribed herein, and for further details publications available fromUnited Technologies Corporation describing the above noted engines areincorporated herein by reference.

The preferred embodiment is shown in FIGS. 3, 4, 5 and 6 which basicallyis a fully cast vane divided into three distinct regions, namely, theleading edge, the trailing edge and the side wall panels. The fully castvane 50 is comprised of the pressure side wall 52, the suction side wall54, the trailing edge 56 and the leading edge 58. The vane may be castin two halves as shown in FIG. 4 and bonded together by any suitablemeans, such as by transient liquid phase which is a well known joiningprocess and then brazed to the platform in a precision die, also a wellknown technique. The ends of rib portions 61 and 63 extending inwardlymate when assembled to form a structural rib to prevent the vane frombulging due to the aerodynamic and pressure loads. Each side wall, i.e.the pressure side wall 52 and suction side wall 54, are cast with aplurality of pockets 60 (see FIG. 5) that is judiciously locatedadjacent the outer surface. A metering slot 62 is formed at the end ofeach pocket for exiting film air adjacent the outer surface of the sidewalls. A plurality of holes 64 are drilled internally of the pocket andcommunicate with the central passages 66 or 68 formed in the vane. Theholes 64 are judiciously located so that cooling air impinges on theback side of the side wall, turns and flows toward the trailing edge inthe mini passage 70 and exits out of metering slot 62 and effectivelyproduces a film of cooling air. Each pocket may include a pedestal orpedestals 74 consistent with each application to enhance heat transfer.As noted in FIG. 5, each row of pockets 60 is arranged so that alternaterows are staggered. As noted, the upper row of pockets is slightlydisplaced relative to the lower row of pockets. Thus assuring that asolid sheet of film cooling air is distributed over the airfoilsurfaces.

The fully cast vane 50 may include inserts or impingement tubes 76 and78 similar to the impingement tubes shown in the prior art (FIGS. 1 and2). A plurality of holes 80 in the walls of the impingement tubes 76 and78 serve to feed the side wall holes of the pockets with the cooling airfrom the compressor section.

As shown in FIG. 6 cool air from the impingement tube flows throughholes 80 to impinge on the back surface of the side wall 52 effectuatingimpingement cooling and convection. The air then flows into the holes 64to impinge on each side of the wall 84 defining the pocket 60 tolikewise maximize cooling effectiveness. The air then turns and flowsleftwardly as viewed in FIG. 6 which is in the direction of the trailingedge and then out of metering slot 62 for laying a film of cool airadjacent the outer surface of the side wall. While effectivelymaximizing the convection process with this invention it is alsopossible to attain a maximum coverage of film cooling air downstream ofthe metering slot that extends over the surface of the airfoil.Conventional trip strips 86 may be included on the back side of the slottrailing edge to enhance heat transfer if so desired.

In this design the leading edge 32 and trailing edge 38 are cooledutilizing conventional technique although in certain embodiments as willbe understood from the description to follow, the side walls are fedwith cool air directly from the central passage in the vane.

The airfoil section of the fully cast vane 50 can be coated with athermal barrier coating similar to that used on the prior art vane asshown by the overlay 90. Since the exit slot flow area is several timeslarger than the metering holes, the metered slots with the coatingprocess are tolerant to TBC use. The TBC build-up closes the slots butnot enough to shift the metering from the internal holes. Since the flowof cooling air is not affected by the TBC, the coating process doesn'tadversely affect the film cooling. In particular, when TBC is a designfeature, the exit slots are oversized such that the application of theTBC coats down the exit slots for an optimum area ratio of the exitslots to the metering holes hence the coolant to gas velocity ratioand/or film cooling effectiveness are optimized.

FIGS. 7, 8, 9, 10, 11 and 12 exemplify vanes incorporating thisinvention that are fabricated from a partially cast process and stampedsheet metal sheaths defining the side wall airfoil section. Similar tothe fully cast vane construction, the embodiments depicted in FIGS. 7and 9 which are fabricated with a single and double liner layerconfiguration, divide the cooling into three distinct regions; namelythe leading edge, the trailing edge and the sidewall panels. Also,similarly these configurations combine backside impingement cooling,convection, surface liner backside impingement and a diffusing channelor metering slot discharging the coolant into the airfoil boundary layerwith an optimum blowing parameter.

In the single layer embodiment depicted in FIG. 7 the inner shell 100which is a structural member is formed in a hollow body defining thecentral passageway 102 and the shape of the airfoil section. The leadingedge 104 with conventional cooling techniques is cast in the shell as isthe trailing edge 106 also with conventional cooling techniques. Theshell includes a plurality of impingement holes that flow cooling airfrom the central passageway 102 which, similar to the vanes describedabove, is in communication with the engine's compressor air exposed tothe inner and outer diameter of the vane through the platforms (see FIG.12, one being shown). These platforms used for attaching the vanes tothe engine's inner cases are cast on the inner and outer diameter of theshell. The outer liner layers defining the outer surface of the airfoilsection are stamp formed out of sheet metal and are contiguous to theouter surfaces of the shell. The sheet metal has stamp formed therein aplurality of shaped dimples defining pockets 112 extending over aportion of the surface of the side walls 108 on both the pressure side114 and suction side 116. Pockets 112 terminate in a slot 120 that isdimensioned to meter cooling flow to provide an optimum blowingparameter and obtain an optimized film of cooling air that flowsadjacent the surface of the airfoil. The drilled holes 122 formed in theshell lead cooling air from the central passageway 102 to impinge on thebackside of the trailing edge of the metered slot 120 in pocket 112 toeffectuate impingement cooling and optimize convection as the cool airflows through the pocket to the metered slot 120.

In assembly, as best seen in FIGS. 7, 11 and 12, the stamped sheet metalliners defining the pressure surface and suction surface are dimensionedto fit into the recess formed between the leading edge 104 and trailingedge 106 adjacent the radial lips 130 and 132 respectively, on thepressure side and 134 and 135 respectively on the suction side. And theinner and outer diameter of the pressure and suction airfoil section fitinto and are trapped in slots 136 and 139 respectively formed on both ofthe platforms (one being shown) (see FIG. 12).

As shown in FIG. 8 the layer defined by the stamp formed sheet metal forthe pressure side 114 and suction side 116 may be coated as in the priorart construction by a suitable thermal barrier coating 138 and like thefully cast vane described above because the slot and holes aresignificantly large and the coating does not adversely affect thecooling aspects.

FIGS. 9, 10, 11 and 12 disclose a multi-layer configuration similar tothe construction described in connection with the FIG. 7 embodiment. Forthe sake of convenience like reference numerals will reflect similarcomponents in each of the embodiments. The outer liner layers 114 and116 are configured similar to the outer liner layer of the single layerembodiment as is the inner structural shell 100. In this embodiment anintermediate liner layer 140 is stamp formed out of sheet metal with adimple 142 that is complementary to the dimple in the outer liner layerand directs cooling air through holes 144 to impinge on the backside ofthe outer liner layer.

The assembly procedure for assembling the multi-layer design is similarto the assembly of the single liner layer design depicted in FIG. 7.

Both the single and multi-layer sheet metal designs permit the use ofdissimilar material for the liner layers and shell. This allows thedesigner a great latitude in the selection of materials such that hightemperature resistant but low strength material (such as wroughtmaterials) can be used for the outer liner layer and a high strength lowtemperature resistant material can be used for the inner shell. Thesedesigns also lend themselves for simplified and less costly repair andreplacement practices. Namely, a liner malfunction can be repaired bysimply replacing the liner rather than the entire vane, as theheretofore practice would be for certain impairments.

Although this invention has been shown and described with respect todetailed embodiments thereof, it will be understood by those skilled inthe art that various changes in form and detail thereof may be madewithout departing from the spirit and scope of the claimed invention.

We claim:
 1. An air cooled stator vane for a gas turbine engine thatincludes means for defining a gas path through said gas turbine enginefor directing a portion of the gas flow ingressing and egressing saidgas turbine engine, said stator vane comprising wall means having anouter surface defining an airfoil section having a suction side andpressure side including a cast wall shell having a plurality of discreteaxially and radially spaced pockets extending over said outer surface ofthe suction side and pressure side of said airfoil section, each of saidpockets including a passageway extending parallel to the flow of theengine's gas path, an impingement hole at one end of said passagewayextending through a portion of said cast wall, a slot formed in saidouter surface adjacent said passageway at the end remote from saidimpingement hole, said impingement hole communicating with a centralpassage centrally disposed internal of said cast wall shell for flowingcooling air from said central passage through said impingement hole andthrough said passageway to discharge into said gas path through saidslot to coalesce the cooling air for flowing a film of cooling air toflow along said outer surface of said airfoil section in a direction ofthe gas path whereby said film of cooling air cools said stator vane. 2.An air cooled stator vane as claimed in claim 1 wherein said impingementhole is angularly disposed relative to said passageway, the flowegressing from said impingement hole being in a direction upstreamrelative to said gas path, wall means defining said passageway alsodefining a turning surface for the flow egressing from said impingementhole to turn in the same direction as said gas path and be in parallelflow relationship thereto.
 3. An air cooled stator vane as claimed inclaim 2 wherein said air cooled stator vane includes an upper end and alower end, each end being opened and in communication with the engine'scooling air, impingement tube inserts in said central passagecommunicating with said each end for distributing cooling air to saidimpingement hole.
 4. An air cooled stator vane as claimed in claim 3wherein said pockets are disposed in rows traversing said suction sideand said pressure side and the pockets in alternate rows are staggeredfrom the pockets in the alternate row.
 5. An air cooled stator vane asclaimed in claim 3 including means for disrupting the flow in saidpassageway for enhancing heat transfer.
 6. An air cooled stator vane asclaimed in claim 5 wherein said flow disrupting means includes apedestal.
 7. For a gas turbine engine, an air cooled stator vaneincluding an inner shell wall member including a leading edge, atrailing edge, a first side wall extending between said leading edge andsaid trailing edge, and a second side wall laterally spaced from saidfirst side wall extending between said leading edge and said trailingedge, a sheet metal sheath contiguous with said first side wall fordefining a suction surface and a second sheet metal sheath contiguous tosaid second side wall for defining a pressure surface, said trailingedge, said leading edge and said first and second sheaths defining anairfoil for said stator vane, a plurality of pockets formed in saidfirst sheet metal sheath and said second sheet metal sheath extendingover the pressure surface and the suction surface, each of said pocketshaving wall means including a back wall defining a passage extendingparallel to said pressure and suction surfaces and having an endterminating at said pressure and suction surfaces, said airfoil having acentral passage for leading cooling air from a source of cooling air insaid engine internally of said airfoil to a location externally of saidairfoil through openings formed in said first and second side wallsthrough openings in said sheet metal sheath through said passage in saidpocket and through a slot formed at said end of said pocket, saidopenings in said sheet metal sheath being an impingement hole extendinginto said pocket at a point remote from said slot whereby the coolingair impinges on the back wall of said pocket and flows out of saidpocket through said slot as a film of cooling air extending over saidairfoil.
 8. For a gas turbine engine as claimed in claim 7 includingmeans in said passage in said pocket for imparting turbulent flow to thecooling air passing therethrough to enhance the heat transfer of saidcooling air and said sheet metal sheaths.